I. Field of the Invention
This invention relates generally to xerographic printing apparatus, and more particularly to an improved flash fusing system for adhering toner particles to a developed image as the sheets pass through the printing system.
II. Discussion of the Prior Art
In prior art xerographic printing systems, a toner consisting of a powdered composition of resins, plasticizers and pigment is electrostatically deposited on an imaging drum and then transferred to a paper sheet. The toner is then fixed with pressure or in a fusion process whereby the toner particles become bonded to the paper sheet. One way to fix the toner is to expose the sheet containing the toner image to radiation energy produced by one or more flash lamps. Xenon flash lamps have proven to be highly suited to the flash fusion operation in that they can produce a high intensity flash and may repeatedly be operated without loss of radiation energy output. Further background concerning the process of flash fusing toner in xerographic printers may be obtained from Marbrouk U.S. Pat. Nos. 3,871,761 and from Garthwaite et al. 4,386,840.
When it is considered that many printing systems must accommodate paper sheets ranging in size from 6 to 81/2 inches in width and from 3 to 16 inches in length, to minimize peak power requirements, it is desirable to control the number of lamps being flashed at the fusion station as a function of paper length. Large sheets, e.g., 81/2.times.16 in. sheets require more energy per sheet to accomplish indelible fusion of the toner. This can be accomplished by including multiple lamps in the fusing station. With larger sheet sizes, the charging circuit for the flash lamps have more time in which to function. With smaller sheet sizes, less energy per sheet is required, but the flash rate must be greater to accommodate the increased flow rate in terms of sheets per unit of time. In conserving peak power, it is desirable to take the maximum time possible for charging the flash lamps, energy storage capacitors to the firing potential for the desired paper size and flow rate.